1. Field of the Invention
The present invention relates to the improvement of a method for producing a valve-regulated lead-acid battery.
2. Description of the Related Art
In order to cope with the recent development of multimedia system, infrastructural improvements in the optical communication network corresponding thereto have been progressing rapidly. An optical communication fiber system is capable of communicating a large amount of data but requires the conversion of optical signal to electrical signal at connecting points. The optoelectronic converter used for this purpose cannot operate without backup power supply against power failure. These converters are mostly used outdoors. Thus, this type of a valve-regulated lead-acid battery used as backup power supply is exposed to very severe temperature atmosphere. In particular, in a high temperature atmosphere in summer time, the storage battery is liable to "dry-up" or "thermal-runaway" due to decomposition of the electrolyte during float charging and thus exhibits impaired battery properties.
The foregoing dry-up which occurs during float charging is a phenomenon in which decomposition causes the electrolyte to lose water content, reducing the discharge capacity of the battery. The foregoing thermal-runaway is a phenomenon in which the rise in temperature is accompanied by the rise in charging current that causes abnormal heat generation of the battery, eventually resulting in dry-up that disables the battery. These phenomena, particularly thermal-runaway, can easily occur when the battery is used at a temperature as high as not lower than 60.degree. C. over an extended period of time. When the battery is used at a temperature as high as not lower than 70.degree. C., these phenomena can occur even in a short period of time. It has thus been desired to develop a battery which can be used in such severe conditions.
The valve-regulated lead-acid battery which is little liable to these phenomena is a battery which shows little rise in float charging current even when used at high temperatures. Such a battery cannot be obtained by the conventional art.
The rise in charging current accompanying the temperature rise is a synergism of the rise in the amount of oxygen produced at the positive electrode by the decomposition of the electrolyte with the rise in the oxygen absorption reaction rate at the negative electrode accompanying the enhancement of the oxygen recombination reaction rate. When the rate of generation of Joule heat accompanying the rise in the reaction heat and charging current becomes greater than the rate of heat dissipation from the battery, the battery temperature rises beyond the ambient temperature. The rise in the battery temperature causes a further rise in charging current that causes a further rise in the battery temperature. Thus, a vicious circle arises, eventually resulting in thermal-runaway.